1. Field of the Invention
The present invention relates to a syringe type pump having a drive mechanism therein for dispensing a liquid at a very slow controlled rate from a syringe barrel of the pump and a mechanism for adjusting the rate thereby to meter the dispensing of the liquid at a desired adjustable rate.
2. Description of the Prior Art
Heretofore various syringe devices and mechanisms associated therewith or incorporated therein for metering fluid from the syringe device have been proposed.
Examples of previously proposed syringe devices and other devices for dispensing liquid at a very slow metered rate are disclosed in the following U.S. patents:
______________________________________ U.S. PAT. NO. PATENTEE ______________________________________ 2,168,437 Buercklin 2,474,496 Rayman 2,545,017 Billingsley 2,605,765 Kollsman 2,706,480 Nensel 2,875,761 Helmer et al. 3,325,061 Ellsworth 3,433,223 Black 4,157,716 Ruegg 4,177,810 Gourlandt 4,190,048 Sampson 4,258,711 Tucket et al. 4,264,241 Portner et al. 4,274,558 Clausen 4,561,856 Cochran ______________________________________
Of these prior art patents, the Cochran U.S. Pat. No. 4,561,856 is the most pertinent and the infusion pump disclosed herein is an improvement over the infusion pump disclosed in the Cochran patent.
The Cochran patent discloses an infusion pump which has a drive mechanism in a housing of the pump. The drive mechanism includes a gas spring at one end of the housing which acts against a piston rod. The piston rod then extends through a timing capsule in the housing and has mounted thereon within the timing capsule a disc which has an outer diameter less than the diameter of the capsule. A viscous fluid is provided in the timing capsule and the other end of the piston rod bears against an outer end of a syringe piston, the inner end of which is received in a syringe barrel.
As the gas spring acts on the first end of the piston rod, it pushes the disc within the timing capsule against the viscous fluid which is caused to flow around the disc and through an annular space between the outer periphery of the disc and the inner diameter of the timing capsule to provide a fixed rate of, and non-adjustable throttling of, movement of the piston rod through the timing capsule which times or dampens the rate at which the piston rod exerts force on the outer end of the syringe piston.
As will be described in greater detail hereinafter, the infusion pump of the present invention, while also using a gas spring, differs from the previously proposed infusion pumps, and in particular the infusion disclosed in the Cochran U.S. Pat. No. 4,561,856, by providing a mechanism by which the gas spring acts directly against the viscous fluid which in turn acts against the outer end of the piston. The flow of the viscous fluid to a location at or adjacent the outer end of the syringe piston so as to transmit pressure thereagainst from the pressure of the gas spring is adjustably throttled, whereby the flow rate of the viscous fluid and thereby the rate at which force is applied against the outer end of the piston (and ultimately the rate at which liquid is dispensed from the syringe barrel) is adjustable. Further, this adjustable control of the flow rate of the viscous fluid, and the resulting dispensing of a liquid solution from the syringe barrel, is easily controllable from outside of the pump and is even adjustable during dispensing of a liquid solution from the syringe barrel.